BEIJING, Jan 27 (Reuters) - Four more Chinese activists went on trial on Monday, accused of disturbing public order after urging officials to reveal their assets, the latest in a string of closely watched prosecutions of anti-graft campaigners.

The trials of members of the "New Citizens' Movement" have sparked criticism from the West and rights groups, as evidence of the ruling Chinese Communist Party's determination to crush any challenge to its rule.

The government has waged a 10-month drive against the movement, founded by Xu Zhiyong, one of China's most prominent rights activists, who was jailed on Sunday for four years.

The four activists put on trial on Monday -- Ding Jiaxi, Li Wei, Zhang Baocheng and Yuan Dong -- advocated working within the system to press for change, including urging officials to publish details of assets.

They were charged with "gathering a crowd to disturb public order", which carries a maximum penalty of five years in prison.

"These individuals, and their prosecution, are part of a pattern of arrests and detentions of public interest lawyers, Internet activists, journalists, religious leaders and others who challenge official Chinese policies and actions," said U.S. diplomat Daniel Delk.

Delk, a second secretary at the U.S. embassy, urged China to release the protesters immediately, lift curbs on their freedom of movement, and guarantee them the protection and freedoms ensured by the country's international human rights commitments.

Police accuse the activists of planning, organising, and carrying out nearly 30 instances of "street political activities", from displaying banners to making speeches urging revelation of assets, according to a copy of Li's arrest notice.

Ding, a lawyer based in Beijing, the capital, was in charge of "organising and overall coordination" of the movement, while Li, who is unemployed, was "responsible for the collection of information and dissemination of labour", the notice said.

Ding's trial was adjourned after he dismissed one of his lawyers, Wang Xing, and another lawyer, Cheng Hai, voluntarily withdrew his defence, because of improprieties in the judicial proceedings, Cheng told Reuters by telephone.

Li's trial was also adjourned after he dismissed his two lawyers, said one of them, Wang Quanzhang.

"From now on, at least the trial has stopped," Wang said. "If we had continued, it would have been finished today and by tomorrow, or within two days, there could be a sentence."

Ding and Li will both get 15 days to select new lawyers, according to Cheng and Wang.

Zhang also dismissed his two lawyers, said Zhou Ze, one of the lawyers.

"He basically does not want this form of playacting by the court," Zhou said, adding that the court had refused to let defence witnesses testify.

Court officials and police refused to let diplomats from eight countries observe the trials on Monday, said Raphael Droszewski, a first secretary at the European Union delegation to China.

Officials turned away the European Union officials, and American diplomats who arrived earlier were told there were not enough seats, he added.

China has detained at least 20 campaigners for asset disclosure by officials, though not all belong to the New Citizens' Movement.

Two activists stood trial on Thursday in Beijing. Three went on trial in December and face more than 10 years in prison if convicted.

Sunday's verdict against Xu is "what Chinese society needs," said the Global Times tabloid owned by Chinese Communist Party mouthpiece The People's Daily.

"Chinese society hopes for stability and its maintenance of a vigilant attitude towards various signs of social unrest is universal," the newspaper said. (Editing by Clarence Fernandez)